Superjunction structures for power devices and methods of manufacture

ABSTRACT

In a general aspect, a power device can include at least one N-type epitaxial layer disposed on a substrate and a plurality of N-pillars and P-pillars that define alternating P-N-pillars in the at least one N-type epitaxial layer. The power device can also include an active region and a termination region, where the termination region surrounds the active region. The alternating P-N-pillars can be disposed in both the active region and the termination region, where the termination region can include a predetermined number of floating P-pillars.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present disclosure incorporates by reference the commonly assignedU.S. patent application Ser. No. 12/234,549 filed Sep. 19, 2008,entitled “Superjunction Structures for Power Devices and Methods ofManufacture,” as if set forth in full in this document, for allpurposes.

BACKGROUND

The present invention relates in general to semiconductor technology andin particular to power semiconductor devices such as transistors anddiodes and their methods of manufacture.

The key component in power electronic applications is the solid-stateswitch. From ignition control in automotive applications tobattery-operated consumer electronic devices, to power converters inindustrial applications, there is a need for a power switch thatoptimally meets the demands of the particular application. Solid-stateswitches including, for example, the power metal-oxide-semiconductorfield effect transistor (power MOSFET), the insulated-gate bipolartransistor (IGBT) and various types of thyristors and rectifiers havecontinued to evolve to meet this demand. In the case of the powerMOSFET, for example, double-diffused structures (DMOS) with lateralchannel (e.g., U.S. Pat. No. 4,682,405 to Blanchard et al.), trenchedgate structures (e.g., U.S. Pat. No. 6,429,481 to Mo et al.), andvarious techniques for charge balancing in the transistor drift region(e.g., U.S. Pat. No. 4,941,026 to Temple, U.S. Pat. No. 5,216,275 toChen, and U.S. Pat. No. 6,081,009 to Neilson) have been developed, amongmany other technologies, to address the differing and often competingperformance requirements.

Some of the defining performance characteristics for the power switchare its on-resistance, breakdown voltage and switching speed. Dependingon the requirements of a particular application, a different emphasis isplaced on each of these performance criteria. For example, for powerapplications greater than about 300-400 volts, the IGBT exhibits aninherently lower on-resistance as compared to the power MOSFET, but itsswitching speed is lower due to its slower turn off characteristics.Therefore, for applications greater than 400 volts with low switchingfrequencies requiring low on-resistance, the IGBT is the preferredswitch while the power MOSFET is often the device of choice forrelatively higher frequency applications. If the frequency requirementsof a given application dictate the type of switch that is used, thevoltage requirements determine the structural makeup of the particularswitch. For example, in the case of the power MOSFET, because of theproportional relationship between the drain-to-source on-resistanceRds-on and the breakdown voltage, improving the voltage performance ofthe transistor while maintaining a low Rds-on poses a challenge. Variouscharge balancing structures in the transistor drift region have beendeveloped to address this challenge with differing degrees of success.

Device performance parameters are also impacted by the fabricationprocess. Attempts have been made to address some of these challenges bydeveloping a variety of improved processing techniques.

Whether it is in ultra-portable consumer electronic devices or routersand hubs in communication systems, the varieties of applications for thepower switch continue to grow with the expansion of the electronicindustry. The power switch therefore remains a semiconductor device withhigh development potential.

BRIEF SUMMARY

In accordance with one aspect of the invention, a power device includesa semiconductor region which in turn includes a plurality of alternatelyarranged pillars of first and second conductivity type. Each of theplurality of pillars of second conductivity type further includes aplurality of implant regions of the second conductivity type arranged ontop of one another along the depth of pillars of second conductivitytype, and a trench portion filled with semiconductor material of thesecond conductivity type directly above the plurality of implant regionsof second conductivity type.

In accordance with another aspect of the invention, a power deviceincludes: an active region and a termination region surrounding theactive region, and a plurality of pillars of first and secondconductivity type alternately arranged in each of the active andtermination regions, each of the plurality of pillars of secondconductivity type in the active and termination regions furtherincluding a plurality of implant regions of the second conductivity typearranged on top of one another along the depth of the pillars of secondconductivity type, and a trench portion filled with semiconductormaterial of the second conductivity type directly above the plurality ofimplant regions of second conductivity type.

In accordance with another aspect of the invention, a method for formingpillars of alternating conductivity type in a power device includes:forming a plurality of epitaxial layers of a first conductivity typeover a substrate; forming a plurality of implant regions of a secondconductivity type in each of a predetermined number of the plurality ofepitaxial layers; forming trenches extending into the upper-most one ofthe plurality of epitaxial layers; and filling the trenches withsemiconductor material of the second conductivity type, wherein theplurality of implant regions of second conductivity type in thepredetermined number of the plurality of epitaxial layers are verticallyaligned with corresponding ones of the trenches so that thesemiconductor material filling the trenches together with the pluralityof implant regions of second conductivity type in the predeterminednumber of the plurality of epitaxial layers form a plurality of pillarsof second conductivity type, and those portions of the plurality ofepitaxial layers separating the plurality of pillars of secondconductivity type from one another form a plurality of pillars of firstconductivity type.

In accordance with another aspect of the invention, a method for formingpillars of alternating conductivity type in a power device includes:forming a first epitaxial layer of a first conductivity type over asubstrate; forming a lower portion of a plurality of deep trenches inthe first epitaxial layer; filling the lower portion of the plurality ofdeep trenches with semiconductor material of a second conductivity type;forming a second epitaxial layer of first conductivity type over thefirst epitaxial layer; forming an upper portion of the plurality of deeptrenches in the second epitaxial layer directly over the lower portionof the plurality of deep trenches so that each lower portion and acorresponding upper portion of the plurality of deep trenches togetherform one of the plurality of deep trenches; and filling the upperportion of the plurality of deep trenches with semiconductor material ofsecond conductivity type, wherein the semiconductor material filling thelower and upper portions of the plurality of deep trenches form aplurality of pillars of second conductivity type, and those portions ofthe first and second epitaxial layers separating the plurality ofpillars of second conductivity type from one another form a plurality ofpillars of first conductivity type.

In accordance with another aspect of the invention, a method for forminga power field effect transistor includes: forming an N-type epitaxiallayer over a substrate; forming one or more P-type epitaxial layers overthe N-type epitaxial layer; forming a plurality of trenches extendingthrough the one or more P-type epitaxial layers; filling the pluralityof trenches with N-type semiconductor material; forming P-type bodyregions in the one or more P-type epitaxial layers; forming N-typesource regions in the P-type body regions; and forming gate electrodesadjacent to but insulated from the P-type body regions and the N-typesemiconductor material, the gate electrodes overlapping with the N-typesource regions, wherein the plurality of trenches filled with N-typesemiconductor material form N-pillars, and those portions of the one ormore P-type epitaxial layers separating the N-pillars form P-pillars.

In accordance with another aspect of the invention, a power field effecttransistor (FET) includes: an N-type epitaxial layer over a substrate;one or more P-type epitaxial layers over the N-type epitaxial layer; aplurality of trenches extending through the one or more P-type epitaxiallayers, the plurality of trenches being filled with N-type semiconductormaterial; P-type body regions in the one or more P-type epitaxiallayers; N-type source regions in the P-type body regions; and gateelectrodes adjacent to but insulated from the P-type body regions andthe N-type semiconductor material, the gate electrodes overlapping withthe N-type source regions, wherein the plurality of trenches filled withN-type semiconductor material form N-pillars, and those portions of theone or more P-type epitaxial layers separating the N-pillars formP-pillars.

In accordance with another aspect of the invention, a method for forminga power field effect transistor includes: forming one or more epitaxiallayers of a first conductivity type over a substrate; forming aplurality of lower trenches extending through the one or more epitaxiallayers; filling the plurality of lower trenches with semiconductormaterial of a second conductivity type; forming one or more epitaxiallayers of the second conductivity type over the one or more epitaxiallayers of first conductivity type; forming a plurality of upper trenchesextending through the one or more epitaxial layers of the secondconductivity type; filling the plurality of upper trenches withsemiconductor material of the second conductivity type, wherein theplurality of lower trenches and the plurality of upper trenches areoff-set from one another along the lateral dimension.

In accordance with another aspect of the invention, a power field effecttransistor (FET) includes a semiconductor region including a pluralityof alternately arranged pillars of first and second conductivity type,wherein each of the pillars of the first conductivity type has a middlesection that is wider than its upper and lower sections, and each of thepillars of the second conductivity type has a middle section that isnarrower than its upper and lower sections.

In accordance with another aspect of the invention, a method for forminga superjunction structure in a power device includes: forming one ormore epitaxial layers of a first conductivity type over a substrate;forming a plurality of trenches extending in the one or more epitaxiallayers; lining the sidewalls and bottom of the trenches with a anepitaxial layer of a second conductivity type; forming a dielectriclayer in the plurality of trenches over the epitaxial layer of secondconductivity type; and filling the plurality of trenches with conformalmaterial.

In accordance with another aspect of the invention, a method for forminga superjunction structure in a power device includes: forming one ormore epitaxial layers of a first conductivity type over a substrate;forming a plurality of trenches extending in the one or more epitaxiallayers; filling each trench with an epitaxial layer of a secondconductivity type such that only a center portion of each trench alongthe top of the trench remains unfilled; and filling the center portionof each trench along the top of the trench with a dielectric material.

In accordance with another aspect of the invention, a method for forminga superjunction structure in a power device includes: forming one ormore epitaxial layers of a first conductivity type over a substrate;forming a plurality of trenches extending in the one or more epitaxiallayers; lining sidewalls and bottom of the plurality of trenches with afirst epitaxial layer of a second conductivity type; filling each trenchwith a second epitaxial layer of the second conductivity type such thatonly a center portion of each trench along the top of the trench remainsunfilled; and filling the center portion of each trench along the top ofthe trench with a dielectric material.

In accordance with another aspect of the invention, a power deviceincludes a plurality of trenches extending in one or more epitaxiallayers of a first conductivity type, the plurality of trenches beingfilled with a first epitaxial layer of a second conductivity type, asecond epitaxial layer of the second conductivity type, and a layer ofinsulating material, the first epitaxial layer lining the trenchsidewalls and bottom, the second epitaxial layer extending over andbeing in direct contact with the first epitaxial layer, and the layer ofinsulating material extending over and being in direct contact with thesecond epitaxial layer, the first epitaxial layer, the second epitaxiallayer, and the third layer of insulating material in each trench forminga pillar of second conductivity type, and those portions of the one ormore epitaxial layers separating the pillars of second conductivity typeforming pillars of first conductivity type such that the pillars offirst and second conductivity type form pillars of alternatingconductivity type.

In accordance with another aspect of the invention, a power deviceincludes at least first and second N-type epitaxial layers extendingover a substrate, and a plurality of trenches extending in the secondN-type epitaxial layer, the plurality of trenches being filled with afirst epitaxial layer, a second P-type epitaxial layer, and a thirdlayer of conductive material, the first epitaxial layer lining thetrench sidewalls and bottom, the second P-type epitaxial layer extendingover and being in direct contact with the first epitaxial layer, and thethird layer of conductive material extending over and being in directcontact with the second P-type epitaxial layer, the first epitaxiallayer, the second P-type epitaxial layer, and the third layer ofconductivity type in each trench forming a P-pillar, and those portionsof the at least first and second N-type epitaxial layers separating theP-pillars forming N-pillars such that the P-pillars and the N-pillarsform pillars of alternating conductivity type.

In accordance with another aspect of the invention, a method for formingpillars of alternating conductivity type in a power device includes:forming at least first and second N-type epitaxial layers over asubstrate; forming a plurality of trenches extending in the secondepitaxial layer; and filling the plurality of trenches with a firstepitaxial layer, second P-type epitaxial layer, and a third layer ofconductive material, the first epitaxial layer lining the trenchsidewalls and bottom, the second P-type epitaxial layer extending overand being in direct contact with the first epitaxial layer, and thethird layer of conductive material extending over and being in directcontact with the second P-type epitaxial layer, the first epitaxiallayer, the second P-type epitaxial layer and the third layer ofconductive material in each trench forming a P-pillar, those portions ofthe at least first and second N-type epitaxial layers separating theP-pillars forming N-pillars such that the P-pillars and the N-pillarsform pillars of alternating conductivity type.

In accordance with another aspect of the invention, a power deviceincludes: one or more N-type epitaxial layers extending over asubstrate; a plurality of trenches extending into the one or more N-typeepitaxial layers, the plurality of trenches being filled with P-typesilicon material, the P-type silicon material in the plurality oftrenches forming P-pillars, those portions of the one or more N-typeepitaxial layers separating the P-pillars forming N-pillars such thatthe N-pillars and the P-pillars form alternating P-N-pillars; and anactive region and a termination region surrounding the active region,wherein the alternating P-N-pillars are disposed in both the activeregion and the termination region, the termination region includes apredetermined number of floating P-pillars, and each N-pillar locatedbetween two adjacent ones of the predetermined number of floatingP-pillars includes a N-type surface region along its upper surface, theN-type surface region having a lower doping concentration than the restof the N-pillar in which it is formed.

In accordance with another aspect of the invention, a power deviceincludes: one or more N-type epitaxial layers extending over asubstrate; a plurality of trenches extending into the one or more N-typeepitaxial layers, the plurality of trenches being filled with P-typesilicon material, the P-type silicon material in the plurality oftrenches forming P-pillars, those portions of the one or more N-typeepitaxial layers separating the P-pillars forming N-pillars such thatthe N-pillars and the P-pillars form alternating P-N-pillars; an activeregion and a termination region surrounding the active region, whereinthe alternating P-N-pillars are disposed in both the active region andthe termination region, the alternating P-N-pillars in the terminationregion surround the active region in a concentric fashion and include apredetermined number of floating P-pillars, each floating P-pillarincludes a P-type ring along its top; a plurality of field platesdisposed in the termination region over but insulated from the one ormore N-type epitaxial layers, the plurality of field plates surround theactive region in a concentric fashion; and a plurality of contactsconfigured so that each of the plurality of contacts makes contactbetween one of the plurality of field plates and one or more of theP-type rings, the plurality of contacts being disposed directly above acorresponding one of the predetermined number of floating P-pillars.

In accordance with another aspect of the invention, a power deviceincludes an active region surrounded by a termination region, and aplurality of trenches extending into one or more epitaxial layers of afirst conductivity type, the plurality of trenches being filled withsilicon material of a second conductivity type, the silicon material ofa second conductivity type in the plurality of trenches together withportions of the one or more epitaxial layers separating the plurality oftrenches from one another forming a plurality of concentricoctagon-shaped pillars of alternating conductivity type extendingthrough the active region and the termination region, wherein four ofthe eight legs of each of the plurality of concentric octagon-shapedpillars have a different length than the other four legs, and sidewallsof the plurality of trenches along all eight legs of the plurality ofconcentric octagon-shaped pillars have the same plane direction.

In accordance with another aspect of the invention, a method of forminga power device having an active region surrounded by a terminationregion, the method comprising: forming a plurality of trenches in one ormore epitaxial layers of a first conductivity type; and filling theplurality of trenches with silicon material of a second conductivitytype, the silicon material of a second conductivity type in theplurality of trenches together with portions of the one or moreepitaxial layers separating the plurality of trenches from one anotherforming a plurality of concentric octagon-shaped pillars of alternatingconductivity type extending through the active region and thetermination region, wherein four of the eight legs of each of theplurality of concentric octagon-shaped pillars have a different lengththan the other four legs, and sidewalls of the plurality of trenchesalong all eight legs of the plurality of concentric octagon-shapedpillars have the same plane direction.

In accordance with another aspect of the invention, a power deviceincludes an active region surrounded by a termination region, aplurality of stripe-shaped pillars of alternating conductivity typeextending through the active region, and a plurality of octagon-shapedpillars of alternating conductivity type extending through thetermination region in a concentric fashion, surrounding the activeregion.

In accordance with another aspect of the invention, a power deviceincludes: an active region surrounded by a termination region; aplurality of pillars of alternating conductivity type arranged in aconcentric fashion in the active and termination regions; a plurality ofpolysilicon gates arranged in concentric fashion in the active region;an outer metal gate runner extending along an outer perimeter of thetermination region in a concentric fashion, the outer metal gate runnerbeing connected to a gate pad; and a plurality of supplementary metalgate runners directly connected to the outer metal gate runner, andextending from the outer metal gate runner toward a center of the activeregion but terminating before reaching the center of the active region,wherein a first group of the plurality of the polysilicon gates directlyconnects to all of the plurality of supplementary metal gate runners,and a second group of the plurality of the polysilicon gates directlycontact only two of the plurality of supplementary metal gate runners.

In accordance with another aspect of the invention, a power deviceincludes: an active region and a termination region surrounding theactive region; a plurality of pillars of alternating conductivity typearranged in a concentric fashion in both the active and the terminationregions; a plurality of polysilicon gate stripes extending through theactive and termination regions; and a gate runner metal extending alongan outer perimeter of the termination region, the plurality ofpolysilicon stripes connecting to the gate runner metal along theiropposite ends.

In accordance with another aspect of the invention, a method for formingpillars of alternating conductivity type in a power device, the methodcomprising: forming one or more N-type epitaxial layers over asubstrate; forming P-type body regions in the one or more N-typeepitaxial layers; forming gate electrodes extending adjacent to butbeing insulated from the one or more N-type epitaxial layers by a gatedielectric; after forming the P-type body regions and the gateelectrodes, forming a plurality of deep trenches extending in the one ormore N-type epitaxial layers; and filling the plurality of deep trencheswith P-type silicon to form a plurality of P-pillars, those portions ofthe one or more N-type epitaxial layers separating the plurality ofP-pillars forming N-pillars such that the P-pillars and the N-pillarsform pillars of alternating conductivity type.

In accordance with another aspect of the invention, a high voltagedevice includes: one or more N-type epitaxial layers extending over asubstrate; a plurality of trenches extending into the one or more N-typeepitaxial layers, the plurality of trenches being filled with P-typesilicon material, the P-type silicon material in the plurality oftrenches forming P-pillars, those portions of the one or more N-typeepitaxial layers separating the P-pillars forming N-pillars such thatthe N-pillars and the P-pillars form alternating P-N-pillars; aplurality of P-wells each formed in an upper portion of one of theP-pillars; and an anode terminal comprising a Schottky barrier metaldirectly contacting a top surface of the N-pillars to form a Schottkycontact therebetween, the Schottky barrier metal further directlycontacting the P-wells.

In accordance with another aspect of the invention, a high voltagedevice includes: one or more N-type epitaxial layers extending over asubstrate; a plurality of trenches extending into the one or more N-typeepitaxial layers, the plurality of trenches being filled with P-typesilicon material, the P-type silicon material in the plurality oftrenches forming P-pillars, those portions of the one or more N-typeepitaxial layers separating the P-pillars forming N-pillars such thatthe N-pillars and the P-pillars form alternating P-N pillars; an N-typeepitaxial layer extending over the alternating P-N Pillars; and an anodeterminal comprising a Schottky barrier metal directly contacting a topsurface of the N-type epitaxial layer to form a Schottky contacttherebetween, the N-type epitaxial layer separating the Schottky barriermetal from the P-pillars so that the P-pillars float.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C show three different layout configurations for asuperjunction power devices;

FIG. 2 shows a simplified cross section view of a superjunction FET;

FIG. 3 shows a simplified cross section view along a portion of a diewhere the active region transitions to termination region throughtransition region, in accordance with an embodiment of the invention;

FIGS. 4A-4H are simplified cross section views depicting various stepsin an exemplary process for forming the pillar structure shown in FIG.3;

FIGS. 5A-5G are simplified cross section views showing variousembodiments in which the flexibility provided by combining thetrench-fill process with the multiple Epi and implant process isadvantageously exploited to obtain performance improvements;

FIGS. 6A-6B are simplified cross section views showing a process forforming P-pillars using a two-step pillar process;

FIGS. 7A-7D, 8A-8D, 9A-9B and 10A-10B are simulation resultsillustrating the impact of various process parameters on the degree ofelectric field concentration along the trench depth;

FIGS. 11A and 11B show a simplified cross section view whereN-enrichment regions are formed at the bottom of N-filled trenches tocreate a local charge imbalance, and the corresponding electric fieldcurve, respectively;

FIGS. 12A and 12B show another simplified cross section view withN-enrichment regions at the bottom of N-pillars to create a local chargeimbalance, and the corresponding electric field curve, respectively;

FIGS. 13A-13B are simplified cross section views showing a three steptrench fill process used in forming a super junction device that is freeof voids;

FIGS. 14 and 15 show simplified cross section views of superjunctionpower devices which minimizes formation of voids in the trench fillprocess;

FIGS. 16A-16C, 17 and 18 are simplified cross section views showingvarious embodiments of super-junction devices with pillars ofalternating conductivity type;

FIGS. 19A-19L are simplified cross section views showing various stagesof a process for forming a super junction trench-gate MOSFET;

FIG. 20 is simplified cross section view used to illustrate the processfor forming the planar-gate variation of the trench-gate MOSFET in FIGS.19A-19L;

FIGS. 21 and 22 are simplified cross section views along a portion ofthe die where the active region transitions into the termination region;

FIG. 23 is a simplified cross section view of a superjunction powerdevice where field plates are electrically connected to theircorresponding floating P-pillars;

FIG. 24A is a top layout view of a corner region of a super junctionpower device;

FIG. 24B is an expanded view of the corner of the termination region ofthe top layout view in FIG. 24A;

FIGS. 25A-25D are simplified cross section views showing variousembodiments of super-junction high voltage merged PiN Schottkyrectifiers;

FIGS. 26A-26B are simplified cross section views showing two additionalembodiments of super junction high voltage Schottky rectifiers;

FIGS. 27A and 27B are respectively top view of a die layout diagram andtop view of a wafer where the wafer flat extends parallel to thelaterally extending pillars in FIG. 27A;

FIG. 28 is a top view of a die layout diagram illustrating rotation ofthe die for the purpose of eliminating the non-uniform epi filling dueto variations in plane direction;

FIG. 29 is a top layout view of a corner of a super-junction powerMOSFET with striped active P-pillars surrounded by concentrictermination P-pillars;

FIG. 30 is a top view of a fully concentric layout design where asupplementary metal gate runner is bussed through a center portion ofthe die to provide metal connection to the concentric polysilicon gates;

FIG. 31A shows a top layout view of a fully concentric design with agate runner design that provides a more balanced gate propagation delaythroughout the die;

FIG. 31B is an expanded view of an inner portion of the top view in FIG.31A;

FIG. 31C is an expanded view of the upper right quadrant of the dieshown in FIG. 31A; and

FIG. 32 shows a top layout view of a fully concentric pillar design withstripe polysilicon gates.

DETAILED DESCRIPTION

The power switch can be implemented by any one of power MOSFET, IGBT,various types of thyristors and rectifiers and the like. Many of thenovel techniques presented herein are described in the context of thepower MOSFET and Schottky rectifiers for illustrative purposes. It is tobe understood however that the various embodiments of the inventiondescribed herein are not limited to the power MOSFET and Schottkyrectifiers and can apply to many of the other types of power switchtechnologies, including but not limited to, for example, IGBTs and othertypes of bipolar switches and various types of thyristors andrectifiers. Further, for the purposes of illustration, the variousembodiments of the invention are shown to include specific P and N typeregions (e.g., for an n-channel MOSFET). It is understood by thoseskilled in the art that the teachings herein are equally applicable todevices in which the conductivities of the various regions are reversed.

In the super junction technology, the alternating P/N-pillars in theactive and termination regions may be arranged in a number of differentlayout configurations. FIGS. 1A-1C show three such layoutconfigurations. In FIG. 1A, P/N-pillars 102 and 104 in both activeregion 108 and termination region 106 are arranged in a concentricconfiguration (hereinafter referred to as “full concentric”configuration); in FIG. 1B, P/N-pillars 112 and 114 in both activeregion 118 and termination region 116 are arranged in a parallel (orstriped) configuration (hereinafter referred to as “full parallel”configuration); and in FIG. 1C, P/N-pillars 122 and 124 in active region128 are arranged in a parallel (or striped) configuration, andP/N-pillars 122 and 124 in termination region 126 are arranged in aconcentric configuration (hereinafter referred to as“parallel-concentric” configuration). Each of these layoutconfigurations has its own merits and drawbacks. Some of the inventionsand embodiments described herein address various drawbacks of theselayout configurations.

The full concentric configuration in FIG. 1A enjoys uniform chargebalance throughout active region 108 and termination region 106, but theactive channel area may be reduced because the gate feeds must extendinto the interior of active area 108 to feed the concentric activepolysilicon gates. The channel may need to be removed at the corners toeliminate areas of lower threshold voltage and prevent parasitic NPNturn-on. Thus, as the die size is reduced, the penalty in on-resistance(Rds-on) attributed to these corners in the active area may becomegreater.

The full parallel configuration in FIG. 1B also enjoys uniform chargebalance throughout the active and termination regions but without theRds-on penalty of the full concentric configuration. However, theP/N-pillar design in the full parallel configuration may be limited toan N-rich balance condition to insure that the P-pillars extending outinto termination area 116 from active area 118 become fully depletedsomewhere along their length. By using concentric pillars for thetermination, as in FIG. 1C, the electric field can be distributed acrossthe termination region without full pillar depletion.

In the design where pillars (e.g., P-pillars) are formed using a trenchetch and fill process, corners of the concentric pillars may bedifficult to etch and fill resulting in voids in the epi fill that causecharge imbalance. These corners may thus become areas of high electricfield stress. If they are shorted to source potential, either of theFIG. 1A and FIG. 1C layout configurations may have a lower breakdownvoltage at these corners. In the parallel-concentric configuration shownin FIG. 1C, these corners may be moved outside active area 128 wherethey can float and are thus not fixed at source potential therebyminimizing or eliminating them as a source of localized lower breakdownvoltage. Also, the active channel area can be maximized and gate feedsused that are more conventional only requiring a perimeter gate runnerto make connection to the active polysilicon gates.

In order to achieve good Unclamped Inductive Switching (UIS)characteristics, it is desirable to design the device so that breakdownfirst occurs in the active region as opposed to any other region of thedevice including the termination region. One way to achieve this is tomake sure that all regions of the device have sufficiently higherbreakdown voltage than the active area by locally modifying the chargebalance in these regions. FIG. 2 shows an embodiment where this isachieved. In FIG. 2, P-pillars 230, 236 in both active region 204 andtermination region 202 may have the same width W3 and similar dopingprofiles. N-type mesa regions 232, 234 (alternatively referred to asN-pillars in this disclosure) in active region 204 and terminationregion 202 may be grown with the same epitaxial layer or layers.

Using known techniques, mesa width W1 and P-pillar width W3 as well asthe doping profiles in P-pillars 230, 236 and N-type mesas 232, 234 maybe designed to achieve a charge balance condition resulting intermination region 202 having a higher breakdown voltage than activeregion 204. In contrast, mesa width W2 in active region 204 may beadjusted to obtain a different charge balance condition that results ina lower breakdown voltage than other areas of the device includingtermination region 202. In one embodiment, mesa width W2 in activeregion 204 may be made smaller than mesa width W1 in termination region202 so that active region 204 is more P-rich. In another embodiment,mesa width W2 in active region 204 may be made greater than mesa widthW1 in termination region 202 so that active region 204 is more N-rich.These techniques ensure that breakdown occurs in active region 204 firstthus resulting in a more stable breakdown characteristic and a moreuniformly distributed current flow during a UIS event. Accordingly, boththe breakdown and UIS characteristics of the device are improved. Notethat an N-rich active region may result in a improved (lower) Rds-on atthe expense of UIS performance, and a P-rich active region may provide abetter UIS performance at the expense of Rds-on. Depending on the designgoals, one approach may be preferred to the other. A number oftechniques for achieving various performance improvements are describednext.

FIG. 3 shows a cross section view along a portion of a die where activeregion 301 transitions to termination region 302 through transitionregion 304. In this exemplary embodiment, transition P-pillars 329A arebridged to the first contacted P-pillar 329B in active region 301through a diffusion region 342 marked as PIso. This bridging diffusionmay extend over N-type mesa regions 333A. In this and other embodimentsdisclosed herein, the N-type mesa regions separating the P-pillars mayalso be referred to as “N-pillars.” When N-type mesa regions 333A intransition region 304 have the same or smaller width than activeN-pillars 333B, an increase in P charge in transition region 304 occurs.This increase in P charge can reduce the breakdown voltage below that ofactive area 301. To compensate for this increase in P charge, the widthof N-pillars 333A in transition region 304 may be made greater than thewidth of N-pillars 333B in the active region. This can ensure that thebreakdown voltage in transition region 304 remains higher than in activearea 301. In the embodiment shown in FIG. 3, transition region 304 isdefined by the span of the bridging diffusion 342.

As with the FIG. 2 embodiment, the width of all P-type pillars 329A,329B, 329C in all regions (the termination, transition and activeregions) may be substantially the same, and the width of terminationmesa regions 333C may be greater than the width of the active mesaregions 333B. However, the width of termination mesa regions 333C may begreater than, the same as, or smaller than the width of transition mesaregions 333A. In active region 301, in one embodiment, P-pillars 329Bmay have the same width and may be spaced from one another by the samedistance. However, in another embodiment, the width of P-pillars 329B inactive region 301 may be smaller than the spacing between them, thusproviding a N-rich condition in the active region. In one embodiment,the active and transition N-pillars and P-pillars may be stripe-shapedwith termination N-pillars and P-pillars surrounding the active andtransition regions in a concentric fashion similar to the layoutconfiguration shown in FIG. 1C. In yet another embodiment, the active,transition, and termination N-pillars may be concentric similar to thelayout configuration shown in FIG. 1A.

In the designs where the pillars (e.g., P-pillars) are formed by etchingdeep trenches and filling them with silicon, as for example in highvoltage super junctions designs, process reliability may be directlyrelated to the trench depth to width ratio (i.e., the trench aspectratio). For higher trench aspect ratios, epi filling of the trenchesbecomes more difficult. FIG. 3 shows a technique whereby P-pillars thatextend deep into the drift region are formed without requiring deeptrenches.

In FIG. 3, a multi-epi process with multiple aligned implantations iscombined with a trench process to form all P-pillars 329A, 329B, 329C.As can be seen, each P-pillar includes three P-implant regions 335A,335B, 335C stacked on top of each other, as well as a trench-filledportion 337 along the upper portion of the P-pillar. Along eachP-pillar, the three P-implant regions 335A, 335B, 335C and the uppertrench-filled portion 337 correspond to separate N-epi layers. That is,in the exemplary embodiment shown in FIG. 3, four N-epi layers are usedto form the P-pillars. More or fewer than four epi layers may be useddepending on the design goals.

The technique exemplified by the FIG. 3 embodiment provides a number ofadvantages. First, the trench etch depth is substantially reduced thusallowing for reduced trench CD and easier trench filling. Also, the cellpitch can be reduced due to the trench etch angle. That is, the trenchesare etched with a taper from bottom to top, thus resulting in a widertrench width at the top. This allows the trenches to be fully filledwithout the risk of pinch off at the top creating voids in the pillar.Having a shallower trench etch reduces the width of the trench at thetop which is a function of the tangent of the etch angle. Consequently,the width of the pillar at the top is smaller and the shallower trenchescan be made with a smaller etch CD because they are easier to fill. Thusa smaller cell pitch and a lower Rds-on can be obtained. Further, as isdescribed more fully in connection with FIGS. 5A through 5G below, thistechnique advantageously: (1) allows use of different P implant CDs foractive and termination P-pillars to insure that break down occurs in theactive area first, and (2) allows adjusting the P implant CDs in theactive region to insure that the avalanche breakdown occurs well belowthe junction formed by the P-type body regions and the N-type driftregion.

Before turning to FIGS. 5A to 5G, an exemplary process for forming thepillar structure shown in FIG. 3 will be described with references toFIGS. 4A to 4H. FIG. 4A shows N+ starting substrate 404. In FIG. 4B, afirst N-epi layer 407A may be grown using conventional techniques. InFIG. 4C, a P-implant may be carried out to form P-implant regions 401A.A conventional masking and implant process may be used to form P-implantregions 401. In FIG. 4D, the steps corresponding to FIG. 4C are repeatedtwo more times to form second and third N-epi layers 407B, 407C and thecorresponding P-implant regions 401B, 401C, followed by formation of afourth and thicker N-epi layer 407D. The second to fourth N-epi layersmay be formed using conventional techniques. The second to fourth N-epilayers may be formed with a uniform, stepped, or graded dopingconcentration. As will be discussed further below, different implantdoping concentration and/or energy may be selected in forming eachP-implant region 401A, 401B, 401C in order to obtain the desired chargedimbalance condition along the pillar length and/or depth.

In FIG. 4E, trenches 403 may be patterned and etched deep enough toreach the uppermost P-implant regions 401C. Backside alignmenttechniques may be used to ensure alignment of trenches 403 withP-implant regions 401C. In FIG. 4F, trenches 403 may be filled withP-epi 425 using known techniques. In FIG. 4G, P-epi 425 may beplanarized using, for example, a conventional chemical mechanicalpolishing (CMP) process. In FIG. 4H, P-type body region 438, N+ sourceregions 418, the P+ heavy body regions as well as the gate structure andits overlying layers may be formed using known techniques. While in theprocess depicted by FIGS. 4A-4G, a separate N-type buffer layer is notincorporated between the substrate and the first N-epi layer 407A (as isdone in FIG. 3), such buffer layer can be incorporated by forming asuitable N-epi layer before forming N-epi layer 407A in FIG. 4C.Alternatively, N-epi layer 407A can be made thicker to account for thebuffer layer.

As can be seen, this process yields a super junction device withP-pillars that are formed from a combination of multiple P-implantregions 401A, 401B, 401C and a relatively shallow trench-filled portion403. Accordingly, the trench etch depth is substantially reduced thusallowing for reduced trench CD and easier trench filling. This techniquealso provides a number of other advantages over conventional techniques,some of which will be discussed with reference to the embodiments shownin FIGS. 5A-5G.

FIGS. 5A-5G show various embodiments in which the flexibility providedby combining the trench-fill process with the multiple Epi and implantprocess is advantageously exploited to obtain performance improvements.FIG. 5A is a cross section view that is similar to FIG. 3 except that alarger P-implant CD is used in forming the bottom-most P-implant region535A of active P-pillars 529B than that used in forming the bottom-mostP-implant regions of transition P-pillars 529A and termination P-pillars529C. In this manner, the charge imbalance at the bottom of the activeP-pillars is made greater than the charge imbalance at the bottom of thetermination and transition P-pillars, thus ensuring that the break downfirst occurs in the active region.

FIG. 5B shows a variation of the FIG. 3 embodiment where P-implantregions 555A, 555B along P-pillars in the active, transition andtermination regions are floating (i.e., P-implant regions 555A, 555B donot merge). This can be achieved by carefully controlling the P-implantdose and energy in the process steps corresponding to FIGS. 4C and 4D.Floating the pillar regions allows for reduced charge balancesensitivity because these regions can assume a potential similar to thefloating pillar regions in the termination. FIG. 5C shows anotherembodiment that is similar to that in FIG. 5B except that a largerP-implant CD is used in forming the bottom-most P-implant regions 555Ain the active P-pillars as compared to that used in forming thebottom-most P-implant regions 555A in the transition and terminationP-pillars. Similar to the FIG. 5A embodiment, the greater chargeimbalance in the active region due to the larger P-implant regions 502forces the break down to occur in the active region.

In the FIGS. 5A and 5C embodiments, the larger P-implant regions may beformed for every other active P-pillar as opposed to all activeP-pillars. This technique is advantageous in that the impact of thelarger P-implant regions on current flow (e.g., pinching off the currentpath at the bottom of the P-pillars) is reduced thus improving Rds-on.The larger P-implant regions could also be formed at the bottom of everythird active P-pillar or every fourth active P-pillar or some otherpattern depending on the avalanche current and as long as breakdownoccurs in a uniform manner in the active region.

FIG. 5D shows a cross section view of yet another embodiment which issimilar to that shown in FIG. 3 except that multiple N-implant regions572A, 572B, 572C are formed in between the P-implant regions 535A, 535B,535C. These N-implant regions enable better control of charge balanceand imbalance as well as make the pillars N rich at the bottom. Havingthe N rich imbalance at the bottom is another method of moving theavalanche location deeper in the silicon without penalizing Rds-on as aresult of pillar pinch off. Referring to FIGS. 4C and 4D, N-implantregions 572A, 572B, and 572C can be formed immediately before orimmediately after forming the corresponding P-implant regions usingknown techniques. Referring back to FIG. 5D, while the N-implant regions572A, 572B, 572C and the P-implant regions 535A, 535B, 535C are formedin a manner that provides similar charge balance characteristics in theactive, transition and termination regions, in the embodiment shown inthe FIG. 5E, a smaller N-implant CD is used in forming the lower-mostN-implant regions 572A in the active region as compared to thelower-most N-implant regions 572A in the transition and terminationregions, thereby forcing break down in the active region. The smallerN-implant regions 572A in the active region may alternatively be formedat the bottom of every other active N-pillar (instead of each and everyactive N-pillar as shown in FIG. 5E). In yet another embodiment shown inFIG. 5F, the bottom-most N-implant region may be eliminated altogetherin the active region by blocking the N-implant in the active regiononly. Alternatively, the bottom-most N-implant region may be eliminatedfrom every other active N-pillar.

FIG. 5G shows yet another embodiment in which a larger P-implant CD isused for the lower-most P-implant regions 535A in the active P-pillarsthan that used in the termination and transition regions, and thebottom-most N-implant regions are eliminated only in the active region.Of the various embodiments, this embodiment provides the most P-richcondition at the bottom of the active P-pillars. Other permutations canbe envisioned in view of the various embodiments disclosed herein. Forexample, the larger P-implant regions in FIG. 5G can be formed at thebottom of every other active P-pillar to obtain better Rds-on, or inFIG. 5G, instead of fully eliminating the bottom-most N-implant region,smaller N-implant regions (such as regions 572A in 5E) can be used toimprove Rds-on. Further, the P-implant regions and/or N-implant regions,or select groups of them, shown in the various embodiments may be formedso that they do not extend along the full length of the P-pillar (e.g.,into the page). Also, while the cross section views in FIGS. 3 and 5A-5Gshow the mesa widths in the active region to be different than the mesawidths in the transition and termination regions, in one embodiment, allmesa widths in the active, transition and termination regions are thesame, and the bottom-most P-implant regions in the active region and/orthe bottom-most N-implant regions in the active region are manipulatedas outlined in the various embodiments described above to insure thatthe active region has a lower break down voltage than the terminationregion. It is also noted that the various embodiments described abovemay be implemented using any of the three layout configurations shown inFIGS. 1A-1C.

While the embodiments described with reference to FIGS. 3, 4A-4H and5A-5G disclose techniques whereby the trench etch depth is substantiallyreduced thus allowing for easier trench filling, another technique forachieving the same is shown in FIGS. 6A-6B.

FIGS. 6A-6B are cross section views showing a process for formingP-pillars using a two-step pillar process. In FIG. 6A, a first N-epilayer 604 is grown over a highly doped substrate 602 using knowntechniques. A bottom portion 606A of a deep trench 606 is formed infirst epi layer 604, and then filled with P-type silicon material 608Ausing conventional methods. A planarization process (e.g., chemicalmechanical polish) may be carried out to planarize the top surface ofthe silicon before the next process step of forming the second N-epilayer 609 is carried out. Second epi layer 609 is formed over firstepitaxial layer 604 using conventional techniques. A top portion 606B ofdeep trench 606 is then formed in second epi layer 609, and then filledwith P-type silicon material 608B using conventional methods. Back-sidealignment techniques may be used to ensure that top and bottom trenches606A, 606B are properly aligned.

Next, A planarization process may be carried out to planarize the topsurface of the silicon before the subsequent steps. A post bake (e.g.,at temperature of 1200 degree C. and 60 minutes) may be carried out toanneal out the defects in the two epi layers. Further processing may becarried out next to form the surface structures. For example, in thecase of a MOSFET, as shown in FIG. 6B, P-type body region 610, N+ sourceregions 614, P+ heavy body regions 612 as well as the gate structure andits overlying layers may be formed using known techniques. The two-steppillar process depicted by FIGS. 6A-6B may be expanded to includeadditional epi, trench etch and trench fill steps, for example, forhigher voltage devices in which the trenched pillars extend even deeper.

This technique provides a number of advantages. By forming and fillingthe deep trench in multiple steps, filling the deep trench is madeeasier. Also, this technique can easily be scaled to accommodate highervoltage devices. That is, depending on the target breakdown voltage andthe corresponding trench depth, the number of epi layers andcorresponding trench etch and fill steps can be increased. Additionally,this technique provides significant flexibility by allowing independentselection of thicknesses and doping profiles for the two N-epi layers,as well as independent selection of doping profiles for the two trenchfills. This flexibility enables more precise control of the electricfield characteristics along the depth of deep trenches 600. For example,the degree of field concentration, as well as the electric field profile(e.g., flat or double peak) and the position of the peak electric field,can be controlled by adjusting the thicknesses of the epi layers and thedoping profiles of the epi layers and the trench fill material.

For example, the simulation results in FIGS. 7A-7D illustrate the impactof the doping concentration of the trench fills on the degree ofelectric field concentration along the trench depth (in thesesimulations, the thicknesses and doping concentration of the two N-epilayers are not changed). In these figures, t1 and t2 indicate thethicknesses of the bottom epi 604 (FIG. 6A) and top epi 609 (FIG. 6),respectively; N1 and N2 indicate the doping concentrations of the bottomepi 604 and top epi 609, respectively; and P1 and P2 indicate the dopingconcentration of the P-type silicon material 608A in the bottom portion606A of deep trench 606 and the P-type silicon material 608B in the topportion 606B of deep trench 606, respectively. As another example, thesimulation results in FIGS. 8A-8D illustrate the impact of the dopingconcentration of the trench fills on the location of the peak electricfield (in these simulations, similar to those in FIGS. 7A-7D, thethicknesses and doping concentration of the two N-epi layers are notchanged). The simulation results in FIGS. 9A-9B illustrate yet anotherexample where the various parameters and physical dimensions aremanipulated to create a double peak in the electric field, thusincreasing the break down voltage. The simulation results in FIGS.10A-10B illustrate still another example where an even higher breakdownvoltage can be obtained by using the appropriate thicknesses for the epilayers and doping concentrations for the trench fill material (it isnoted that this particular simulation result shows that, as compared tostandard 900V MOSFETs, the parameters and dimensions identified in thetable in FIG. 10B yield a substantially lower Rds-on—a factor of 10—forthe same break down voltage). Thus, the location of peak impactionization and the avalanche point along the depth of the pillar can becontrolled so as to be below the body junction.

As discussed above, it is advantageous to induce the onset of avalanchebreakdown along the bottom half of the pillars away from the body-driftjunction. FIG. 11A shows a cross section view in accordance with anexemplary embodiment of the invention where N-enrichment regions 1105may be formed at the bottom of N-filled trenches 1107 to create a localcharge imbalance thereby inducing the onset of avalanche breakdown atthe pillar bottoms. This characteristic of the FIG. 11A structure can beseen from the electric field curve shown in FIG. 11B. The electric fieldcurve shows the electric field profile along the depth of the crosssection view in FIG. 11A. As can be seen, N-enrichment regions 1105cause the electric field peak to occur near the bottom of the pillars.N-enrichment regions 1105 preferably have a higher doping concentrationthan N-pillars 1108 to create the charge imbalance. Since the electricfield profile and thus the breakdown voltage is a function of the totalN-type and P-type charge in both pillars, the N-pillars can be moreheavily doped and made narrower thus reducing the pitch. This benefit isrealized because the impact of the lateral diffused compensation fromthe P-pillar doping into the N-pillar is minimized.

The structure in FIG. 11A may be formed as follows. An N-epi layer 1104may be grown over N+ substrate 1102 using conventional techniques. AnN-enrichment implant may be carried out to form N-enrichment regions1105 where bottoms of N-pillars 1108 will terminate. A conventionalmasking and implant process may be used to form N-enrichment regions1105. The implant doping concentration and energy may be set inaccordance with the target charge imbalance condition at the pillarbottoms. An alternate method for forming N enrichment regions 1105 is togrow an N-type epi layer, etch the pillar trenches and then implant thebottom of the trenches with N enrichment dopants.

One or more P-epi layers 1106 may be grown over N-epi layer 1104 usingconventional techniques. The one or more P-epi layers 1106 may be formedwith a uniform, stepped, or graded doping concentration. Trenches 1107may be patterned and etched deep enough to reach N-enrichment regions1105. Backside alignment techniques may be used to ensure alignment oftrenches 1107 with N-enrichment regions 1105. Trenches 1107 may befilled with N-epi using known techniques. The N-epi used to fill thetrenches need not be fully planarized since any portions of N-epiremaining over the P-epi 1106 can be used in forming the top structureof the power device. Alternatively, the N-epi used to fill the trenchesmay be planarized using, for example, a conventional chemical mechanicalpolishing (CMP) process. P-body regions 1110, N+ source regions 1114, P+heavy body regions 1112 as well as gate structure 1116 and its overlyinglayers (not shown) may be formed using known techniques. In oneimplementation, P-body regions 1110, source regions 1114 and heavy bodyregions 1112 are all formed after gate structure 1116 is formed.

In another embodiment shown in FIG. 12A, one or more P-epi layers 1206 amay be grown over N-epi layer 1204 using convention techniques. The oneor more P-epi layers 1206 a may have a uniform, stepped, or gradeddoping concentration. Lower trenches 1207 maybe patterned and etcheddeep enough to reach N-enrichment regions 1205. Lower trenches 1207 maybe filled with N-epi 1208 a using know techniques. One or more N-epilayers 1208 b is then grown over the one or more P-epi layers 1206 a andthe N-epi filled lower trenches 1207, using conventional techniques. Theone or more N-epi layers 1208 b may have a uniform, stepped, or gradeddoping concentration. Upper trenches 1209 maybe patterned and etcheddeep enough to reach the one or more P-epi layers 1206 a. Upper trenches1209 may be filled with P-epi 1206 b using know techniques. The uppertrenches may be aligned to the lower trenches using backside alignmenttechniques or can be run perpendicular to the lower trenches.

As can be seen, N-pillars 1208 have a reverse taper along their upperhalf. P-epi 1206 b used to fill upper trenches 1209 may be planarizedusing, for example, a conventional CMP process. P-body regions 1210, N+source regions 1214, P+ heavy body regions 1212 as well as gatestructure 1216 and its overlying layers (not shown) may be formed usingknown techniques. In one implementation, P-body regions 1210, sourceregions 1214 and heavy body regions 1212 are all formed after gatestructure 1216 is formed. An advantage of this structure is that thewider P-pillar at the surface pushes the avalanche point down so thatavalanche occurs below the surface P-body region and the increasedelectric field at the bottom due the N-enrichment causes the peakelectric field to occur at the bottom. This characteristic of the FIG.12A structure can be seen from the electric field curve shown in FIG.12B. The electric field curve shows the electric field profile along thedepth of the cross section view in FIG. 12A. The Wider N-Pillar with theN-enrichment at the bottom increases the peak current at which pinch-offoccurs due to JFET effects and lowers Rds-on.

The N-enrichment regions 1105 in FIGS. 11A and 1205 in FIG. 12Aadvantageously induce avalanche breakdown at the bottom of the pillarsand thus result in a device with improved UIS capability. TheN-enrichments may be used in other advantageous ways as well.

As discussed above, device ruggedness can be improved in trench epi fillcharge balance devices by initiating breakdown in the active area andhaving the breakdown voltage be substantially lower than other areas,such as termination regions, gate runner areas, and other areas that arelikely to be a potential source of charge imbalance. In one embodiment,N-enrichment regions may be formed at the bottom of N-pillars in theactive region only. In another embodiment, N-enrichment regions may beformed at the bottom of every other active N-pillar. In otherembodiments, N-enrichment regions may be wider than or narrower than theactive N-pillars or distributed along length of a N-pillar in an uniformor non-uniform pattern. In yet another variation, the distribution ofN-enrichment may not need to be the same for every P-pillar. In yetanother embodiment, the N-enrichment regions may be formed in a blanketmanner (i.e., adjacent N-enrichment regions merge together) in theactive region. Alternatively, the N-enrichment regions may be formed ina blanket manner across both the active and termination regions.

In accordance with other variations of the FIGS. 11A and 12A technique,regions of P-enrichment (not shown) are formed at the bottom of theP-pillars or at the bottom of the N-pillars to disrupt charge balanceand thereby create a location of lower breakdown voltage so thatavalanche initiates at this localized area. The P-enrichment regions maybe implemented in both the active and termination regions, thus ensuringthat breakdown occurs near the bottom of the pillars and is far from thesilicon surface. Alternatively, the P-enrichment regions may beimplemented in the active region only, so that the charge balance isdisrupted in the active region to ensure breakdown in the active region.The P-enrichment regions may be wider or narrower than the P-pillars ordistributed along a length of a P-pillar in a uniform or non-uniformpattern. In another variation, the P-enrichment regions may be formed atthe bottom of every other P-pillar in the active region. In yet anothervariation, the distribution of P-enrichment may not need to be the samefor every P-pillar.

The technique depicted in FIGS. 11A, 12A and its various embodimentsdescribed above may be implemented using any of the three layoutconfigurations shown in FIGS. 1A-1C.

In the super junction approach where P-pillars are formed using deeptrenches, it is difficult to prevent formation of voids in the epimaterial that is typically used to fill the deep trenches. Such voidsare undesirable because they can lead to reliability and leakageproblems. FIGS. 13A-13B are cross section views showing a three steptrench fill process used in forming a super-junction device that is freeof voids.

In FIG. 13A, one or more N-type epitaxial layers, marked in the figureas N epi 1302, is (are) formed over a suitable substrate (not shown).Trenches 1304 are etched in N epi 1302 using known techniques. P-typeepitaxial layer 1306 lining the trench sidewalls and bottom is formedusing conventional methods. Next, dielectric layer 1308 (e.g., grown ordeposited oxide) is formed over P-epi layer 1306 in trenches 1304 usingknown methods. Finally, the central remaining portion of trenches 1304is filled with a conformal material such as amorphous silicon orpolysilicon that is doped or undoped using known methods. This techniqueeliminates formation of voids since epi is used to only partially fillthe trench, and a conformal material, such as polysilicon, is used tofill the difficult-to-fill central portion of deep trenches. Thevoid-free filling of deep trenches is achieved while preserving theability to carefully set the P-charge for charge balance purposes viaP-liner 1306. That is, using conformal material 1310 to fill the centralportion of the trenches eliminates formation of voids while P epi liner1306 enables accurate control of the P-charge. Dielectric layer 1308 inturn, advantageously, serves as a cap layer preventing out-diffusion ofP-dopants from P-epi liner 1306 to poly fill 1310. Thus charge balancebecomes independent of trench width.

In FIG. 13B, the surface structure of the device, in this case a planargate MOSFET, is formed. Incorporating the three step trench fill processin other MOSFET structures (e.g., trench gate variation) or other typesof super junction devices (e.g., planar gate or trench gate IGBTs) wouldbe obvious in view of this disclosure. In FIG. 13B, P-type body regions1312, N+ source regions 1314 and P+ heavy body regions 1316 are formedin N epi 1302 using conventional techniques. The gate structure,including gate dielectric 1318 and gate electrodes 1320 are formed usingknown processes. Source metal 1322, contacting source regions 1314,heavy body regions 1316 and poly fill 1310, is formed using knowntechniques. A back-side drain metal (not shown) contacting the substrate(not shown) is formed in accordance with conventional methods.

As stated earlier, it is difficult to fill deep trenches with epiwithout formation of voids. Voids can lead to reliability and leakageissues and are thus undesirable. FIG. 14 shows a simplified crosssection view of a superjunction power device which minimizes formationof voids in the trench fill process. Trenches 1408 (one of which isshown in FIG. 14) are formed in one or more layers of N-epi 1402. Thoseportions of the one or more N-epi layers 1402 that separate adjacenttrenches 1408 from one another, form N-pillars. A thick P-epi liner 1404is grown in trenches 1408. P-epi liner 1404 sets the P charge for theP-pillars. Most of trench 1408 is filled by P-epi liner 1404, and itsthickness is selected so that the top of trenches 1408 remain open afterthe epi growth process. A dielectric material 1406 is then used to fillthe rest of the trench. In one embodiment, dielectric material 1406comprises high quality thermal oxide. The thermal oxide fill helpsimprove reliability. Also, the P charge can be easily controlled byP-epi liner 1404. The remaining structural details of the power device(not shown), and the manner of forming them, may be similar to thoseshown in FIG. 13B.

Another embodiment directed to eliminating formation of voids in deeptrenches is shown in FIG. 15. This embodiment is similar to the FIG. 14embodiment except that the fill process includes forming an additionalepi layer in the trenches. In FIG. 15, trenches 1508 (one of which isshown in FIG. 15) are formed in one or more layers of N-epi 1502. Thoseportions of the one or more N-epi layers 1502 that separate adjacenttrenches 1508 from one another, form N-pillars. A first P-epi liner 1510lining the trench sidewalls and bottom is formed in trenches 1508.Trenches 1508 are then mostly filled by another lighter doped P-epilayer 1504. The thicknesses of P-epi layers 1510 and 1504 are selectedso that the top of trenches 1408 remain open after the epi fill process.A dielectric material 1506 is then used to fill the rest of the trench.In one embodiment, dielectric material 1506 comprises high qualitythermal oxide. The remaining structural details of the power device (notshown), and the manner of forming them, may be similar to those shown inFIG. 13B.

FIG. 16A shows a cross section view of yet another super junction devicewith pillars of alternating conductivity type. In this embodiment, theP-pillars include 2 differently doped P epi layers: an outer P− epilayer 1610A, and a center P epi layer 1610C. These two epi layers may beformed by successively filling the trench with P epi layers ofincreasing doping concentration. An advantage of such P-pillar structureis that the width of the N-pillars is kept intact since the outer P epilayer 1610A is lightly doped and thus the lateral diffusion of P-typedopant into adjacent N-pillars has minimal or no impact on the increasein the N-pillar resistivity. Keeping the width and resistivity of theN-pillars intact improves Rds-on.

The FIG. 16A structure further includes a retro-graded N-pillar. As canbe seen, the N-pillar includes, from bottom to top, N+ region 1618, Nepi layer 1606 and N− epi layer 1608. Such retro-graded N-pillaradvantageously reduces the peak electric at the P-N junction formed bythe P-body and N-drift regions, and lowers the Rds-on. The N+ region1618 of the N-pillar can be formed as follows. Prior to forming N− epilayer 1604 over substrate 1602, a heavy dose of arsenic is implantedinto region 1604 of substrate 1602 using a mask. During subsequent heatcycles, the arsenic in heavily implanted region 1604 up-diffuses into N−epi layer 1604, thus forming N+ region 1618.

The remaining portions of the FIG. 16A structure may be formed asfollows. N epi layer 1606 and N− epi layer 1608 are formed over N− epilayer 1604 using conventional techniques. Deep trenches extending intoN− epi layer 1608 and N epi layer 1606 are formed using known methods.The deep trenches terminate in or prior to reaching N− epi layer 1604.The deep trenches are then filled with P epi layers 1610A and 1610Cusing conventional epi processes. The remaining surface structures ofthe super junction device, in this case a trench gate MOSFET, are formedusing known techniques. The gate trenches housing gate electrodes 1612are formed in N− epi 1608, followed by forming a thick bottom oxidealong the trench bottom. Gate dielectric 1616 is formed along the trenchsidewalls followed by forming recessed gate electrodes 1612 in the gatetrenches. Source regions 1614 are formed adjacent the gate trenches, anda source metal contacting source regions 1614 and P epi layers 1610A,and 1610C is formed along the top surface of the structure. A drainmetal (not shown) contacting substrate 1602 is formed along thebackside.

FIG. 16B shows a cross section view of another super-junction devicewith pillars of alternating conductivity type. In this embodiment, theP-pillars include 2 differently doped epi layers: an outer P+ epi layer1611A and a center P− epi layer 1611C. An advantage of such P-pillarstructure is that the P-pillar charge is set by the outer P+ epi layer1611A which lines the trench. Thus, the effect of the charge variationof the P-pillar at the top and the bottom remains consistent and isindependent of the trench angle which makes the trench wider at the top.Keeping the P-pillar charge the same from top to bottom of the trenchreduces the variation in charge imbalance resulting from the trenchangle, which in turn results in less variation of breakdown voltage.

FIG. 16C shows a cross section view of yet another super junction devicewith pillars of alternating conductivity type. In this embodiment, theP-pillars include 3 differently doped P epi layers: outer P− epi layer1613A, center P− epi layer 1613C and middle P epi layer 1613B sandwichedby outer epi layer 1613A and center epi layer 1613C. These three epilayers may be formed by successively filling the trench with P epilayers of different doping concentrations. Such P-pillar structureprovides a compromise between FIGS. 16A and 16B. This structure offersthe advantage of the FIG. 16A structure, namely, the lateral diffusionof P-type dopants into the N-pillars is substantially reduced thusminimizing or eliminating the impact on the N-pillar resistivity. TheFIG. 16C structure also offers the advantage of the FIG. 16B structurein that the effect of the charge variation of the P-pillar at the topand the bottom remains consistent and is independent of the trench anglebecause the P-pillar charge is set by the middle P+ epi layer 1613B.Thus, the FIG. 16C structure has the advantages of reduced breakdownvoltage variation and reduced Rds-on.

FIG. 17 shows a cross section view of yet another super junction devicewith pillars of alternating conductivity type. In this embodiment, theP-pillars include 3 differently doped P epi layers: outer P− epi layer1710A, center P+ epi layer 1710C and middle P epi layer 1710B sandwichedby outer epi layer 1710A and center epi layer 1710C. These three epilayers may be formed by successively filling the trench with P epilayers of increasing doping concentration. An advantage of such P-pillarstructure is that the width of the N-pillars is kept intact since theoutermost P epi layer 1710A is lightly doped and thus out-diffusesminimally. Keeping the width of the N-pillars intact improves Rds-on.

In another embodiment shown in FIG. 18, P-enrichment region 1822 isformed at the bottom of each P-pillar using similar techniques to thosedescribed above for forming N-enrichment regions 1105 in FIG. 11. SuchP-enrichment regions advantageously compensate up-diffusion of dopantsfrom N− epi layer 1604. Many of the same variations discussed above inconnection with N-enrichment regions 1105 in FIG. 11 may be applied tothe FIG. 18 embodiment. Also, enrichment region 1822 can be formed alongthe bottom of the P pillars in the embodiments shown in FIGS. 16A-16Cand 17.

Although epi layer 1610A in FIG. 16A, epi layer 1611C in FIG. 16B, epilayers 1613A, 1613C in FIG. 16C, epi layer 1710A in FIG. 17, and epilayers 1810A and 1810C in FIG. 18 are all shown as P− epi, they could belightly doped N− or intrinsic epi silicon. Further, center layer 1611Cin FIG. 16B, center layer 1613C in FIG. 16C and center layer 1810C inFIG. 18 embodiments need not be from epi, and can instead be fromanother material such as polysilicon.

FIGS. 19A-19L are cross section views showing various stages of aprocess for forming a super-junction trench-gate MOSFET. These figuresshow a portion of the die where active region 1903 transitions intotermination region 1905. In FIG. 19A, N-epi 1902 is formed over asuitable substrate (not shown) using conventional techniques. N-epi 1902may comprise multiple epi layers with different doping concentrations,or may be a single epi layer with graded or uniform dopingconcentration. Using masking layer 1904 (e.g., comprising photoresist),a boron implant process 1906 is then carried out to form P-Iso region1908 in N-epi layer 1902. P-iso region 1908 extends in the transitionand termination regions, and is incorporated for reasons stated above inconnection with FIG. 3, and is formed in a similar manner to that inFIG. 3.

In FIG. 19B, P-iso drive and trench hard mask oxidation are carried outin one process step. Hard mask 1910 (comprising oxide) is then formedover the top surface. Trenches 1912 are defined using photoresist 1911.In FIG. 19C, trenches 1912 are formed in N-epi layer 1902 using knowntechniques. Gate dielectric 1914 is then formed along trench sidewallsand bottom using conventional techniques (e.g., gate oxidation). Priorto forming gate dielectric 1914, a thick bottom dielectric mayoptionally be formed along trench bottoms to reduce the gate to draincapacitance. In FIG. 19D, conventional polysilicon deposition and etchback steps are carried out to form recessed gate electrodes 1916 intrenches 1914.

In FIG. 19E, P-type body regions 1918 are formed in N-epi 1902 usingconventional implant and drive processes. In FIG. 19F, source regions1920 are formed in the active region adjacent active trenches usingconventional implant and drive processes. In FIG. 19G, anoxide-nitride-oxide (ONO) composite layer 1922 is formed using knowntechniques. In one embodiment, the ONO comprises from bottom to top: padoxide 1922A, nitride 1922B, and thick LTO 1922C. Pad oxide 1922A servesas a nitride etch stop in a later process step. In FIG. 19H, deeptrenches 1924 are defined and etched into N-epi 1902 using techniquesdescribed in this disclosure, or using known techniques.

In FIG. 19I, known techniques are used to fill trenches 1924 with P-typesilicon 1926. As can be seen, vertically extending portions 1902A ofN-epi 1902 between adjacent P-filled pillars 1926, form N-pillars.N-pillars 1902A and P-pillars 1926 thus form the super-junctionstructure, namely, the alternating pillars of opposite conductivitytype. In FIG. 19J, the top oxide layer in ONO composite layer 1922 isremoved, defining edge LTO 1922A, and BPSG 1930 is formed over thesurface of the device using conventional processes and then annealed. InFIG. 19K, BPSG 1930 is defined and etched using masking layer 1932(e.g., comprising photoresist) to form contact openings in BPSG 1930.The remaining portions of BPSG 1930 cover the gate electrodes and extendover source regions 1920. A conventional heavy body implant is carriedout to form P+ heavy body regions 1934 through the contact openings.Alternatively, dimples may be etched in body regions 1918, and P-typedopants may then be implanted along the bottom of the dimples to form P+heavy body regions in body regions 1918. The dimples also exposesidewalls of the source regions to which contact can be made by thelater formed source metal. In FIG. 19L, a conventional BPSG reflow iscarried out to round the corners of the dielectric, followed byformation of the various metal layers (e.g., source metal layer 1936 andgate metal layer 19368). A backside metal (e.g., drain metal, not shown)contacting the substrate on the backside of the die is formed usingknown techniques.

In termination region 1905, the P-Iso region 1908, which is electricallyconnected to source metal 1936, connects a number of the P-pillarstogether and thus biases these P-pillars along their tops to the sourcepotential. All termination P-pillars located to the right of P-Isoregion 1908 float, and are marked in FIG. 19L as “floating P-pillars1940.”

As can be seen, P-pillars 1926 are formed relatively late in the processas compared to conventional trenched pillar processes where theP-pillars are formed early in the process. Because the P-pillars areformed late in the process after most of the thermal budget has beencompleted, the out-diffusion of the P-pillar dopants is advantageouslyminimized. This enables use of tighter pitch for P-pillars and resultsin lower Rds-on without compromising breakdown voltage.

The process embodiment depicted by FIGS. 19A-19L is directed to a trenchgate MOSFET however, this process can be modified to implement a planargate MOSFET with the same advantages, as described next. This processwill be described with reference to FIG. 20, which is a cross sectionview of a planar gate MOSFET that is formed using the process that isdescribed next. One or more N-type epitaxial layers 2027A, 2027B areformed over a suitable substrate 2024 using know techniques. P-typeenrichment regions 2021 may optionally be formed in epi layer 2027Aprior to forming epi layer 2027B. As described in connection with otherembodiments, P-enrichment regions 2021 advantageously create more of acharge imbalance at the bottom of the P-pillars, thereby inducing theonset of avalanche breakdown at the bottom of the P-pillars and awayfrom the body-drift junction.

The gate dielectric and the overlying planar gate electrodes 2014 aredefined and formed over N-epi 2027B using known techniques. P-typedopants are then implanted with planar gate electrodes 2014 serving as ablocking layer, followed by a drive step, thus forming P-type bodyregions 2038 in N-epi 2027B. After the drive step, the P-type bodyregions laterally extend under the gate electrodes. Using knowntechniques, source regions 2018 are then defined and formed in bodyregions 2038 adjacent each edge of gate electrodes 2014. A conformallayer, e.g., a nitride layer, (not shown) extending over the gateelectrodes and stepping down between adjacent gate electrodes over thebody and source regions is formed using known techniques. A thick layerof LTO (not shown) is then formed over the nitride layer. The LTO isthen defined and etched to expose silicon surfaces between adjacent gateelectrodes where deep trenches 2003 are to be formed. The LTO wouldcover the source regions 2018. A conventional silicon etch is thencarried out to form deep trenches 2003.

Next, the trenches are filled with P-type silicon using conventionaltechniques. The LTO is removed using the conformal (e.g., nitride) layeras an etch stop. The conformal layer may then be removed or may be leftintact and used as a self alignment spacer to space off a high energy P+implant from the poly gate edges. Dielectric cap 2051 (e.g., comprisingBPSG) covering gate electrodes 2014 is formed using conventionaltechniques. Dielectric cap 2051 form contact openings between adjacentgate electrodes. A heavy body implant is carried out through the contactopenings to form the P+ heavy body regions in body regions 2038 betweenadjacent source regions 2018. The remaining process steps would besimilar to those shown in FIG. 18L and thus will not be described. Ascan be seen, in this planar gate process, as in the trench gate processof FIGS. 18A-18L, the P-pillars are formed late in the process aftermuch of the thermal budget is used, thus minimizing out-diffusion ofP-pillar dopants.

In the process technology where pillars are formed by etching trenchesand filling them with silicon (rather than using the multi-epi process),varying the mesa width is undesirable as it results in non-uniformtrench etch and filling. Therefore, center-to-center pillar spacingneeds to be maintained constant to the extent possible. However, with aconstant pillar spacing other provisions need to be made to obtain thedesired surface electric field profile. FIGS. 21 and 22 are crosssection views showing exemplary embodiments where the desired surfaceelectric profile is obtained using surface N regions and/or surface Pregions.

FIG. 21 shows a cross section view along a portion of the die where theactive region transitions into the termination region. The cross sectionview in FIG. 21 is similar to that shown in FIG. 19L except N− surfaceregions 2142 are formed along the top of those N-pillars 2102A locatedbetween floating P-pillars 2140 in termination region 2105. N− surfaceregions 2142 advantageously serve to spread the surface electric fieldthus improving the break down voltage in the termination region. Allother structural features in the FIG. 21 cross section view are similarto those in FIG. 19L and thus will not be described.

The process steps for forming N− surface regions 2142 can beincorporated in the process sequence depicted by FIGS. 19A-19L asfollows. In FIG. 19A, prior to forming any of the regions along the topsurface, N− surface region 2142 may be formed by growing a lightly dopedN− epitaxial layer over N-epi 1902. The N− epitaxial layer 2142 wouldhave a lower doping concentration than N-epi 1902. Alternatively, N−surface region 2142 may be formed by performing a blanket compensationP-implant into N-epi 1902 so that a top layer of N-epi 1902 is convertedto a lighter doped N− layer. The process sequence as depicted in FIGS.19A-19L would then be carried out to form the MOSFET.

In FIG. 21, the top regions of floating P-pillars 2140 in terminationregion 2105 together with their adjacent N− surface regions 2142 make analready P-rich condition along the pillar tops even more P-rich, thuspotentially lowering the break down voltage in termination region 2105.The surface regions of floating P-pillars 2140 can be compensated toimprove the charge balance along the pillar tops. In one embodiment,after forming the P-pillars as depicted by the process stepscorresponding to FIG. 19I, and before the process steps corresponding toFIG. 19J (i.e., while the top surfaces of all P-pillars are exposed), ablanket compensation N implant is carried out to compensate the topregions of all P-pillars in the active and termination regions. Thus,the blanket compensation N implant into the top regions of all P-pillarsensures that the termination region has a higher break down voltage thanthe active region.

While FIG. 21 shows implementation of the N− surface regions in a trenchgate MOSFET, the N− surface regions may also be incorporated in theplanar gate variation. In the planar gate embodiment however, a JFETimplant carried out only in the active region may be necessary toincrease the doping concentration in the JFET regions which wouldotherwise be made up of the lightly doped N− surface region. The JFETimplant enhances the transistor Rds-on which would otherwise beadversely impacted by the N− surface region. In the process describedabove in connection with the planar gate embodiment shown in FIG. 20,the JFET implant may be incorporated after forming the N− surface regionbut before forming the gate structure.

In the FIG. 22 embodiment, surface P-enrichment regions 2244 are formedalong top surfaces of the P-pillars in termination region 2205. Theactive P-body regions 2218 may extend deeper than P-enrichment regions2244, and may have a higher doping concentration than P-enrichmentregions 2205. The doping and depth of P-enrichment regions 2244 as wellas the doping and depth of N− surface regions 2242 may be designed toobtain a charge balance state resulting in a high breakdown voltage witha low peak electric field and substantially evenly distributed electricfield across the termination region. In one embodiment, it is desirableto have the charge of P-enrichment regions 2244 higher than the chargeof the N surface regions to minimize the peak surface electric field.

In any of the above embodiments, the P-pillars in both the active andtermination regions may be equally spaced from one another so that allN-pillars have the same width.

Conductive field plates are used to spread the electric field moreuniformly in the termination region. It is desirable to electricallyconnect the field plates to the underlying pillars so that they canassume the potential of their corresponding pillar. FIG. 23 shows across section view of a super junction power device where field plates2330 are electrically connected to their corresponding floatingP-pillars 2304 through surface well regions (also referred to as “Prings”) formed along tops of P-pillars 2304. These electricalconnections are made by forming contacts between field plates 2330 andcorresponding well regions through one or more dielectric layers 2332.However, as cell pitch is reduced, forming a contact between the fieldplates and their underlying pillars becomes more difficult. FIG. 24A isa top layout view of a corner region of a super-junction power deviceshowing a technique for contacting field plates to the underlyingpillars for small cell pitches. FIG. 24B is an expanded view of thecorner the termination region of the top layout view in FIG. 24A.

In FIG. 24A, active region 2404 and termination region 2402 aredelineated. The pillar configuration is similar to theparallel-concentric configuration shown in FIG. 1C. That is, theP-pillars in active region 2404 extend parallel to each other, while theP-pillars in termination region 2402 extend in a concentric fashionaround the active region. As shown, contact structures 2406 forelectrically connecting the field plates to the underlying floatingP-pillars are advantageously located directly over the P-pillars wherethe P-pillars make a 90 degrees turn. FIG. 24B will be used to show anddescribe contact structures 2406 in more detail.

In FIG. 24B, P-pillars 2412 are spaced equally from one another in theactive and termination regions. P-rings 2408 are formed along the topsof corresponding P-pillars, and extend in a concentric fashion aroundthe active region similar to the floating P-pillars in which they areformed. In one embodiment, the width of P-rings 2408 gradually decreasesin the direction away from the active region. Field plates 2410 (e.g.,comprising polysilicon) extend over but are off-set relative tocorresponding P-pillars and P-rings so that each of them extendspartially over a corresponding P-pillar and partially over an adjacentmesa region (or N-pillar). Field plates 2410 surround the active regionin a concentric fashion similar to P-rings 2408. While the P-rings areshown in FIGS. 23, 24A and 24B to be centered about the correspondingP-pillars, the P-rings may be off-set to the right or the left relativeto the corresponding P-pillar. The offset P-rings can be advantageouslyused to merge two adjacent P-pillars along the surface.

Contacts 2406 are formed directly above corresponding P-pillars 2412 inthe corner regions where the P-pillars make a 90 degree turn. The cornerregions provide additional space in which contacts 2406 can be formed. Aconductive or semiconductive material 2414 (e.g., a metal) is used tomake the connection between each P-pillar 2412 and the correspondingpolysilicon field plate 2410 through contacts 2406.

In one embodiment, two or more P-rings 2408 physically touch therebymerging the corresponding P-pillars at the surface. This advantageouslyprovides a larger surface area for forming the contacts. This techniqueis particularly useful in designs with tighter cell pitches whereforming one contact per P-pillar can be difficult. In anotherembodiment, the termination N-pillars located between the floatingP-pillars include a lightly doped N− region along their tops similar tothose shown in FIGS. 21 and 22. In yet another embodiment, highly dopedP+ regions are formed in the P-rings to ensure a more robust contactbetween the field plates and the corresponding P-rings. The P+ regionsmay be formed at the same time the P+ heavy body regions are formed inthe active area of device.

The technique described in connection with FIGS. 23 and 24A, 24B may beused in the design of edge termination for any superjunction ornon-superjunction power semiconductor device (e.g., MOSFET, IGBT,diode).

FIGS. 25A-25D are cross section views showing various embodiments ofsuper-junction high voltage merged P-N Schottky rectifiers. Thesefigures show a portion of the die where the active region transitions tothe termination region. In FIG. 25A, active region 2501 includesalternating P-N pillars 2530, 2532. P-pillars 2530 are trench-filledpillars, similar to various other embodiments described herein. P-wells2538 extend along a top side of corresponding P-pillars 2530. P-wells2538 are wider than P-pillars 2530 and extend to a predetermined depthfrom the top silicon surface. A Schottky barrier metal 2571 togetherwith an overlying metal layer 2572 (e.g., comprising aluminum) extendalong the top surface of the top epitaxial layer. Schottky barrier metal2571 and metal layer 2572 together form the anode terminal of theSchottky rectifier. As can be seen, the anode terminal contacts both thetop surface of N-pillars 2532 and the top surface of P-wells 2538. Wherethe anode terminal makes contact with N-pillars 2532, Schottky contactsare formed.

During operation, the alternating P-N pillar structure keeps the highelectric field away from the Schottky surface area, thus reducing thereverse leakage. Additionally, the P-N pillars can support high voltagesthus allowing use of low resistivity N pillars (where the currentflows), thereby reducing the series resistance component of the diodeforward voltage. Moreover, P-wells 2538 serve to pinch off the activeN-pillars near the surface at a lower voltage, which helps to furtherreduce the reverse leakage current. Thus, a high voltage Schottkyrectifier with low forward voltage and low reverse leakage is obtained.

In one embodiment, the active and transition P-N pillars may bestripe-shaped with termination P-N pillars surrounding the active andtransition regions in a concentric fashion similar to the layoutconfiguration shown in FIG. 1C. In yet another embodiment, the active,transition, and termination P-N pillars may be concentric similar to thelayout configuration shown in FIG. 1A. In the latter layoutconfiguration, the gate feed issues associated with MOSFETs is notpresent since there are no gate structures in the Schottky rectifier.

FIG. 25B shows a variation of the FIG. 25A embodiment in which P+contact regions 2506 are formed in P-wells 2538. The anode terminalforms an ohmic contact with P-wells 2538 through P+ contact regions2506. This allows the diode to operate at high current density withlower conduction voltage due to the parallel conduction of the PN diodewhen the forward voltage exceeds the built in potential.

FIG. 25C shows a variation of the FIG. 25B embodiment where P-wells 2538are not included, but P+ contact regions 2506 are included so that theanode terminal makes ohmic contact with P-pillars 2530 along their topsthrough the P+ contact regions 2538. This variant trades off lowerforward voltage for increased leakage resulting from the higher electricfield at the barrier.

FIG. 25D shows a variation of the FIG. 25A embodiment where P-wells2538A have approximately the same width as the P-pillars in which theyare formed. With the width of P-well regions reduced as compared to theFIG. 25A embodiment, the mesa width (N-pillar width) near the surface isincreased thus lowering the forward voltage of the Schottky rectifier.

The MOSFET process described above can be modified in simple ways toform the Schottky rectifiers in FIGS. 25A-25D. For example, the FIG. 25Aembodiment may be obtained by eliminating the source implant from theMOSFET process. The P+ regions in FIGS. 25B and 25C correspond to theheavy body region of the MOSFET. Because of the compatibility betweenthe processes for the MOSFET and the Schottky rectifier, MOSFET (e.g.,FIG. 3) and Schottky rectifier (e.g., FIG. 25A) can be easily integratedin a single die to thereby obtain a SynchFET.

FIGS. 26A and 26B are cross section views showing two additionalembodiments of super-junction high voltage Schottky rectifiers. In FIG.26A, after trench-filled P-pillars 2630 are formed, an N-type epitaxiallayer 2682 is formed over the P-N pillar structure, after which theanode terminal comprising Schottky barrier metal 2671 and an overlyingmetal layer 2672 (e.g., comprising aluminum) is formed over and directlycontacts N-type epitaxial layer 2682. In this embodiment, P-pillars 2630are not connected to the anode terminal and thus float. This embodimentadvantageously lowers the forward voltage of the Schottky rectifier byincreasing the Schottky contact area, and reduces leakage current byusing the floating pillars to deplete the active N-pillars at a lowvoltage.

FIG. 26B shows a variation of the FIG. 26A embodiment where instead ofN-epi layer 2682, an N-implant is performed to thereby form N-implantregion 2684 along the top surface of the P-N pillars. As shown, theanode terminal comprising Schottky barrier metal 2671 and an overlyingmetal layer 2672 (e.g., comprising aluminum) directly contacts N-implantregion 2684.

In FIGS. 25A-25D and 26A-26B, while the P pillars are shown as being ofthe trench filled variety, the pillars can have a lower portion that ismade up of multiple bubble-shaped P-regions, and an upper portion thatis trench filled, similar to P-pillars 329A, 329B, 329C shown in FIG. 3.Furthermore, the transition region 2504, 2604 and termination regions2502, 2602 in FIGS. 25A-25D and 26A-26B are similar to the correspondingregions in FIG. 3, and thus will not be described. The same advantagesobtained in integrating these regions with the active region of theMOSFET in FIG. 3 are realized with the Schottky structure of FIGS.25A-25D and 26A-26B.

A challenge in filling trenches having a high aspect ratio is avoidingformation of voids in the trench or preventing premature epi closurealong the top of the trench due to localized growth near the top cornersof the trench. In superjunction layout configurations where trenchsidewalls have different plane directions, filling trenches with epibecomes even more difficult because the epi filling process is sensitiveto silicon crystal plane direction. For example, the rate at whichepitaxial silicon grows along the <100> plane direction is differentthan the rate at which epitaxial silicon grows along the <110> planedirection. This is more clearly illustrated in FIGS. 27A and 27B. FIG.27A shows a top view of a die layout diagram, and FIG. 27B shows a topview of a wafer where the wafer flat extends parallel to the laterallyextending pillars in FIG. 27A.

FIG. 27A shows a full concentric octagon layout configuration. That is,P-pillars 2710 and N-pillars 2706 in both active region 2712 andtermination region 2714 are concentric octagons. P-pillars 2710 areformed in trenches using techniques disclosed herein. While thesidewalls of vertically and horizontally extending trenches have thesame plane direction, namely, <110>, the diagonally extending trencheshave the <100> plane (this assumes that the die shown in FIG. 27A ispositioned on the wafer so that the horizontally extending trenches runparallel to the wafer flat, as depicted in FIGS. 27A and 27B). Thisvariation in plane direction will result in non-uniform filling of thetrenches.

In accordance with one embodiment, the non-uniform epi filling due tovariations in plane direction can be eliminated by rotating the wafer22.5 degrees. This is illustrated in FIG. 28. As can be seen, byrotating the wafer and thus the dies on the wafer duringphotolithography processing, the dies can all be oriented so that alltrench sidewalls line up along the <(tan 22.5)10> plane direction. InFIG. 28, similar to FIG. 27A, P-pillars 2810 and N-pillars 2806 in bothactive region 2812 and termination region 2814 are concentric octagons,and P-pillars 2810 are formed in trenches using techniques disclosedherein. Alternatively, N-pillars 2806 may be formed in trenches usingtechniques disclosed herein. In one embodiment, the wafer is maintainedin the 22.5 degree rotated position throughout the process sequence. Thestructural details of the power device (e.g., MOSFET, IGBT or rectifier)housed in the die shown in FIG. 28 are not shown, but such details canbe found in other embodiments disclosed herein.

In the FIG. 1C layout design where the striped active P-pillars aresurrounded by termination P-pillars, the sharp corners of the concentricrectangular or square shaped termination pillars are difficult to etchand fill and may result in formation of voids in the epi fill. Suchvoids can cause charge imbalance resulting in localized breakdownvoltage. These voids can also result in areas in the termination regionhaving high electric field stress that become a source of electroninjection into the oxide and a magnet for positive charges, resulting inreliability failures.

FIG. 29 is a top layout view of a corner of a super-junction powerMOSFET with striped active P-pillars 2904 surrounded by concentrictermination P-pillars 2904. In this layout design the sharp corners ofthe concentric termination P-pillars in FIG. 1C are eliminated byforming octagon shaped termination P-pillars. By eliminating the sharpcorners, the concentric termination trenches can be filled withoutformation of voids in the fill material. As can be seen, the corneredges of the octagon shaped termination P-pillars gradually increase inlength in the direction away from the active region. Also, as comparedto the fully concentric octagon design with equal length legs, the FIG.29 layout configuration provides better packing and thus a moreefficient use of silicon.

In FIG. 29, gap region 2908 is formed between an end of active P-pillars2904 and the first concentric P-pillar in termination region 2910. Twofull floating mesa regions (or N-pillars) 2914 are inserted to provideisolation between gap 2708 and corner areas and termination 2910. Thesefeatures reduce the sensitivity to breakdown voltage due to chargeimbalance in this area. In one embodiment, the trench fill processdescribed in connection with the FIG. 28 embodiment is used to furthereliminate the possibility of void formation due to non-uniform epifilling caused by differing plane directions along the terminationtrench sidewalls. That is, prior to filling the trenches, the wafer isrotated 22.5 degrees so that all trench sidewalls line up along the<(tan 22.5)10> plane direction. In one embodiment, the wafer ismaintained in the 22.5 degree rotated position (relative to wafer flat)throughout the process sequence. The structural details of the powerdevice (e.g., MOSFET, IGBT or rectifier) housed in the die shown in FIG.28 are not shown, but such details can be found in other embodimentsdisclosed herein

FIG. 30 is a top view of a fully concentric layout design where asupplementary metal gate runner 3002 is bussed through a center portionof the die to provide metal connection to all the concentric polysilicongates 3008. A cross section view along line A-A′ is also included inFIG. 30. Metal gate runner 3004 extends around the perimeter of the dieand connects to a gate pad (not shown), and to supplementary metal gaterunner 3002. P-pillars 3010, N-pillars 3006 and planar polysilicon gates3008 all extend in a concentric fashion in active region 3012 andtermination region 3014.

Supplementary metal gate runner 3002 extends far enough inside the dieto contact the inner most concentric polysilicon gate. A drawback ofthis gate runner design is that it does not provide a balanced gatepropagation delay. As can be seen, the inner most concentric polysilicongates travel a shorter distance before contacting supplementary metalgate runner 3002 than do the outer most concentric polysilicon gates.The inner concentric polysilicon gates thus exhibit a lower propagationdelay than the outer concentric polysilicon gates. This imbalance inpropagation delays makes it difficult to obtain good switching speedswithout dynamic failure of the device.

FIG. 31A shows a top layout view of a fully concentric design with agate runner design that provides a more balanced gate propagation delaythroughout the die. While FIG. 31A does not show the concentric P and Npillars and the concentric polysilicon gates, these regions of the diein FIG. 31A are similar to those in FIG. 30. Outer metal gate bus 3114extends around the outer perimeter of the die and contacts gate pad3116. Four supplementary metal gate runners 3118A, 3118B, 3118C and3118D extend from outer metal gate bus 3114 toward the center of thedie, but terminate before reaching the die center. In this design, whilea number of the outer concentric polysilicon gates directly tie into thefour supplementary metal gate runners, a number of the inner-mostconcentric polysilicon gates are not directly connected to all of thesupplementary metal gate runners. This can be seen more clearly in FIG.31B which is an expanded view of an inner portion of the top view inFIG. 31A.

In FIG. 31B, the concentric poly gates 3108 as well as the end portionsof supplementary metal gate runners 3118A and 3118B in the active regioncan be seen. Concentric polysilicon gates 3108 encircle a center portionof the die through which polysilicon feed 3120 extends. Polysilicon feed3120 extends laterally to make electrical contact with supplementarymetal gate runner 3118A to the left of the die center, and tosupplementary metal gate runner 3118C (not shown in FIG. 31B) to theright of the die center. As can be seen, none of the supplementary metalgate runners extend all the way to the center of the die. Instead, thelengths to which these four supplementary metal gate runners extend arecarefully selected in order to obtain a more balanced gate propagationdelay among the concentric poly gates 3108. As a result, a number of theinner-most concentric polysilicon gates do not directly tie into all ofthe supplementary metal gate runners.

FIG. 31C is an expanded view of the upper right quadrant of the dieshown in FIG. 31A. FIG. 31C will be used to illustrate how theparticular lengths selected for the supplementary metal gate runners forthis embodiment result in a more balanced propagation delay through theconcentric poly gates. Two measurements are shown. The innermeasurement, marked by reference numeral 3122, measures one half thelength of a concentric gate poly that extends between two supplementarymetal gate runner 3118C to just below the bottom end of supplementarymetal gate runner 3118B (i.e., does not tie into gate runner 3118B),ties into supplementary metal gate runner 3118A (not shown in FIG. 31C),and circles back around to tie into metal gate runner 3118C. That is,the measured concentric gate poly ties into gate runners 3118A and3118C, but not 3118B and 3118D. On the other hand, the outermeasurement, marked by reference numeral 3124, measures a length of theoutermost concentric gate poly connected between two supplementary gaterunners as it circles around the die. The measurements illustrate thatthe portion of the measured inner poly gate that extends betweensupplementary gate runner 3118C and 3118A (i.e., the closest two gaterunner to which it is directly connected) is substantially equal to theportion of the measured outer poly gate that extends betweensupplementary gate runners 3118B and 3118C (i.e., the closest two gaterunners to which it is directly connected). Also, those concentric polygates closer to the center of the die that do not contact any of thefour supplementary metal gate runners have short enough length that thepropagation delay through them would not be very different from theouter concentric poly gates that are tied to two or all four of thesupplementary gate runners.

As can be seen, while this technique does not obtain perfectly equalpropagations delays through all concentric poly gates, it significantlyimproves the imbalance in the gate poly propagation delay that ispresent in the FIG. 30 gate runner design. As FIG. 31A illustrates,while supplementary metal gate runners 3118A, 3118B, 3118C, 3118D extendinto the middle of the die, ample surface area remains for bonding tothe source metal. The technique illustrated in FIGS. 31A-31C can beimplemented in the planar gate variation or the trench gate variation.

FIG. 32 shows a top layout view of a fully concentric pillar design withstripe polysilicon gates. Metal gate runner 3204 extends around theperimeter of the die and connects to a gate pad (not shown). P-pillars3210 and N-pillars 3206 extend in a concentric fashion in active region3212 and in termination region 3214. Polysilicon gates 3208 (which canbe of the planar gate or trench gate varieties) are stripe shaped andextend through both active and termination regions, and contact metalgate runner 3204 along their opposite ends.

This configuration advantageously eliminates the need for thesupplementary gate runner(s) that is needed in the concentric gate polydesign, thus resulting in area savings. While some channel area is lostwhere gate poly stripes 3208 cross over P-pillars 3210, the impact onRds-on due to channel resistance increase is small in high voltagedevices.

While the above provides a complete description of specific embodimentsof the present invention, various modifications, alternatives andequivalents are possible. For example, while some embodiments of theinvention are illustrated in the context of planar gate MOSFETs, thesame techniques could easily be applied to other planar-gate structuressuch as planar gate IGBTs by merely reversing the polarity of thesubstrate from those shown in the figures. Similarly, some of thestructures and process sequences are described in the context ofN-channel FETs, however, modifying these structures and processsequences to form P-channel FETs would be obvious to one skilled in theart in view of this disclosure. Further, the various techniquesdisclosed herein are not limited to planar gate structures and may beimplemented in trench gate MOSFETs, trench gate IGBTs (which have trenchgates), shielded gate MOSFETs or IGBTs (which have trenched gates withunderlying shield electrode(s)), and rectifiers (including Schottkyrectifiers, TMBS rectifiers, etc.).

Additionally, while not specifically called out for each embodiment, thevarious embodiments including many of the termination designs and chargebalance techniques may be implemented in any of the three layoutconfigurations shown in FIGS. 1A-1C. Similarly, many of the embodimentsdisclosed herein including many of the termination designs and chargebalance techniques are not limited in implementation to the trench epifill charge balance process technology, and may also be implemented inthe multi-epi layer pillar process technology. For this and otherreasons, therefore, the above description should not be taken aslimiting the scope of the invention, which is defined by the appendedclaims.

What is claimed is:
 1. A power device comprising: at least one N-typeepitaxial layer disposed on a substrate; a plurality of trenchesextending into the at least one N-type epitaxial layer, the plurality oftrenches being filled with a P-type silicon material, the P-type siliconmaterial in the plurality of trenches defining P-pillars, portions ofthe at least one N-type epitaxial layer separating the P-pillarsdefining N-pillars, such that the N-pillars and the P-pillars definealternating P-N-pillars; an active region; and a termination regionsurrounding the active region, the alternating P-N-pillars beingdisposed in both the active region and the termination region, thetermination region including a predetermined number of floatingP-pillars, each N-pillar located between two adjacent floating P-pillarsof the predetermined number of floating P-pillars including an N-typesurface region disposed along an upper surface, the N-type surfaceregion having a lower doping concentration than a doping concentrationof a remaining portion of the N-pillar in which the N-type surfaceregion is disposed.
 2. The power device of claim 1, further comprising:a P-type body region disposed in the at least one N-type epitaxiallayer; a gate electrode adjacent to but insulated from the P-type bodyregion; an N-type source region disposed in the P-type body region; asource metal electrically contacting the source region; and a P-Isoregion disposed on a surface of the at least one N-type epitaxial layer,at least two P-pillars of the alternating P-N-pillars in the terminationregion being electrically connected to the source metal via the P-Isoregion.
 3. The power device of claim 2, further comprising: a shallowtrench extending into the at least one N-type epitaxial layer; and agate dielectric layer lining a sidewall of the shallow trench, the gateelectrode being disposed in the shallow trench.
 4. The power device ofclaim 2, wherein the gate electrode includes a planar gate electrodedisposed on but insulated from the at least one N-type epitaxial layerby a gate dielectric layer.
 5. The power device of claim 1, wherein eachof at least two P-pillars of the alternating P-N-pillars in thetermination region includes a P-type enrichment region disposed along anupper surface, the P-type enrichment region having a higher dopingconcentration than a doping concentration of a remaining portion of theP-pillar in which the P-type enrichment region is disposed.
 6. The powerdevice of claim 5, further comprising: a P-type body region disposed inthe at least one N-type epitaxial layer; a gate electrode adjacent tobut insulated from the P-type body region; an N-type source regiondisposed in the P-type body region; a source metal electricallycontacting the source region; and a P-Iso region disposed along asurface of the at least one N-type epitaxial layer, at least twoP-pillars of the alternating P-N-pillars in the termination region beingelectrically connected to the source metal via the P-Iso region.
 7. Apower device comprising: at least one N-type epitaxial layer disposed ona substrate; a plurality of trenches extending into the at least oneN-type epitaxial layer, the plurality of trenches being filled with aP-type silicon material, the P-type silicon material in the plurality oftrenches defining P-pillars, portions of the at least one N-typeepitaxial layer separating the P-pillars defining N-pillars, such thatthe N-pillars and the P-pillars define alternating P-N-pillars; anactive region; and a termination region surrounding the active region,the alternating P-N-pillars being disposed in both the active region andthe termination region, the alternating P-N-pillars in the terminationregion concentrically surrounding the active region and Including atleast two floating P-pillars, each of the at least two floatingP-pillars including a P-type ring disposed in an upper portion; aplurality of field plates disposed in the termination region, disposedon but insulated from the at least one N-type epitaxial layer, theplurality of field plates concentrically surrounding the active region;and a plurality of contacts, a contact of the plurality of contactselectrically connecting a field plate of the plurality of field platesand at least one of the P-type rings, the plurality of contacts beingdisposed directly above a corresponding floating P-pillar of the atleast two floating P-pillars.
 8. The power device of claim 7, whereinthe at least two floating P-pillars are electrically contacted atlocations of the at least two floating P-pillars that define arespective corner.
 9. The power device of claim 7, wherein a width ofthe P-type rings gradually decreases in a direction away from the activeregion.
 10. The power device of claim 7, wherein each of the pluralityof field plates is disposed directly above a corresponding floatingP-pillar of the at least two floating P-pillars and directly above anN-pillar adjacent to the corresponding floating P-pillar.
 11. The powerdevice of claim 7, wherein the plurality of contacts are disposedthrough at least one insulating layer that is disposed between theplurality of field plates and the at least one N-type epitaxial layer.12. The power device of claim 7, wherein adjacent P-pillars of theP-pillars in the active and termination regions are equally spaced. 13.The power device of claim 7, wherein the P-type rings are centered abouta corresponding floating P-pillar of the at least two floatingP-pillars.
 14. The power device of claim 7, wherein each P-type ringincludes a highly doped P+ region that defines an electrical contactbetween at least one of the plurality of field plates and the P-typering.
 15. A power device comprising: an active region; a terminationregion surrounding the active region; a plurality of stripe-shapedpillars of alternating conductivity type disposed in and extendingthrough the active region; and a plurality of octagon-shaped pillars ofalternating conductivity type disposed in and extending through thetermination region, the plurality of octagon-shaped pillarsconcentrically surrounding the active region.
 16. The power device ofclaim 15, wherein corner edges of the plurality of octagon-shapedpillars of alternating conductivity type gradually increase in length ina direction away from the active region.
 17. The power device of claim15, wherein the plurality of stripe-shaped pillars includes a pluralityof stripe-shaped P-pillars, and the plurality of octagon-shaped pillarsincludes a plurality of octagon-shaped P-pillars, ends of the pluralityof stripe-shaped P-pillars being spaced from the plurality ofoctagon-shaped P-pillars by a gap region that electrically floats. 18.The power device of claim 15, wherein a first four of eight legs of eachof the plurality of octagon-shaped pillars have a different length thana second four legs of the eight legs, the second four legs beingdifferent than the first four legs.
 19. The power device of claim 15,further comprising a plurality of trenches extending into at least oneepitaxial layer of a first conductivity type, the plurality of trencheshaving a silicon material of a second conductivity type disposedtherein, the silicon material of the second conductivity type disposedin the plurality of trenches, together with portions of the at least oneepitaxial layer separating the plurality of trenches from one another,defining the plurality of octagon-shaped pillars of alternatingconductivity type, sidewalls of the plurality of trenches along alleight legs of the plurality of octagon-shaped pillars having a sameplane direction.
 20. The power device of claim 15, further comprising: abody region of a first conductivity type disposed in the at least oneepitaxial layer; a source region of a second conductivity type disposedin the body region; and a gate electrode extending adjacent to but beinginsulated from the body region, the gate electrode overlapping a portionof the source region.
 21. The power device of claim 4, wherein theplanar gate electrode is a first planar gate electrode, the power devicefurther comprising: a second planar gate electrode laterally spaced fromthe first planar gate electrode, at least one trench of the plurality oftrenches being disposed between the first planar gate electrode and thesecond planar gate electrode.